The present invention relates to a color image processing apparatus which may favorably be applied to an image processing apparatus of a plain paper color copier. Particularly the invention is concerned with and intended for a color image processing apparatus capable of easily ascertaining the condition of an image reading means and the state of the light source and light distribution state, and furthermore capable of eliminating an over-flow in A/D (analog-to-digital) conversion.
In a color image processing apparatus such as a color copier in which a laser beam generator is used, color image information is obtained by separating plural colors on a color document, and color images are recorded according to the color image information.
When color images are recorded, the apparatus can conduct variable magnification processing, partial color conversion processing, and other kinds of image processing by the built-in CPU (Central Processing Unit).
Partial color conversion processing is defined as image compiling processing by which the image information inside or outside the designated area is recorded with the color used to designate the area.
In this type of color copier, it is ascertained by the built-in CPU whether the condition of the components of the copier is adequate or not, and according to the result, the copying operation is stopped or abnormal condition signals are displayed.
In this case, the condition of the components is estimated by the image signals which are read out by an image reading means such as a CCD (Charge-Coupled device) in copying.
In the case of judging by the built-in CPU the condition of components which constitute a copier, particularly the state of a CCD, which is an image reading means, or judging disconnection of the light source for document exposure, for example a tungsten halogen lamp, the CPU can not pass a correct judgment. It is a disadvantage of estimating the condition of the components of a copier.
When the light source circuit is cut off, the image signal level becomes zero. Therefore, it can be surely detected according to the image signal whether the light source is disconnected or not.
However, it is difficult to judge the condition of the CCD. the image reading means. The reason is that the condition of the CCD is judged by a prescribed standard level, but the image signals which form the basis of judgment, differ according to the contents of documents.
These image signals are different from the electrical signals to which the optical images exposed on a document are converted. The signals can be image signals which are boosted by AGC (Automatic Gain Control) or signals to which various kinds of image processing are conducted.
An object of the present invention is to provide a color image processing apparatus which can positively and easily judge the condition of the copier components.
In this type of color copier, a tubular lamp such as a tungsten halogen lamp or a fluorescent lamp which is on the market, is used as the light source to read images.
In a case where a tubular lamp is used, the state of light distribution must be checked. The reason is that images on a document can not be correctly converted to color signals when light distribution is bad.
When copiers were shipped from a factory, the state of light distribution was conventionally checked with a synchroscope. Light distribution had been investigated focusing on one point of the light source. For instance, the investigation has been conducted on the basis of the converted data at the center of the light source.
But it is very difficult in practice to take a synchroscope to the place where a customer is using the apparatus and to inspect light distribution of the light source.
Therefore, when a lens or a CCD. which is an optical reading means, is replaced during maintenance and inspection at the customer's place, it is not easy to confirm the results of light distribution adjustment.
Only light distribution of the light source center is inspected, so light distribution of the total area can not be confirmed.
Accordingly, it is an object of the present invention to provide a color image processing apparatus which can easily check light distribution of the total area.
In this type of image processing, an image signal transferred photoelectrically is converted to a digital signal and various kinds of signal processing are conducted in the form of a digital signal.
Therefore, usually an analog image signal transferred photoelectrically by an image reading means, is amplified to an appropriate level by an amplifier and fed to A/D converter for sampling and quantization. that A/D conversion output in a line, for instance at the center, can become the maximum value.
Level adjustment, a process conducted prior to A/D conversion, is conducted by controlling an amplifier so that A/D conversion in a line, for instance at the center, can become the maximum value.
This is based on a general rule that when a straight light source is used in photoelectric conversion, light distribution of the center is more intense than that of the peripheral portion. Therefore, in the case where a straight light source, light of which is the most intense at the center, is used, there is no problem.
However, some light sources show light distribution patterns in which light from the peripheral portion is more intense than that of the center.
Up to this time, it had been thought that light was always the most intense at the center of the light source. Therefore, the level of photoelectric conversion signal was adjusted according to the photoelectric signal obtained at the center of a line. For that reason, in the above-mentioned case. A/D conversion output overflowed and the photoelectric signal could not be correctly A/D converted.
Another object of this invention is to provide a color image processing apparatus which can correctly conduct A/D conversion processing even when a light source with a biased light distribution is used, and in which A/D conversion output does not overflow.